title: Aphanomyces euteiches cell wall fractions containing novel glucan-chitosaccharides induce defense genes and nuclear calcium oscillations in the plant host Medicago truncatula.
abstract: N-acetylglucosamine-based saccharides (chitosaccharides) are components of microbial cell walls and act as molecular signals during host-microbe interactions. In the legume plant Medicago truncatula, the perception of lipochitooligosaccharide signals produced by symbiotic rhizobia and arbuscular mycorrhizal fungi involves the Nod Factor Perception (NFP) lysin motif receptor-like protein and leads to the activation of the so-called common symbiotic pathway. In rice and Arabidopsis, lysin motif receptors are involved in the perception of chitooligosaccharides released by pathogenic fungi, resulting in the activation of plant immunity. Here we report the structural characterization of atypical chitosaccharides from the oomycete pathogen Aphanomyces euteiches, and their biological activity on the host Medicago truncatula. Using a combination of biochemical and biophysical approaches, we show that these chitosaccharides are linked to β-1,6-glucans, and contain a β-(1,3;1,4)-glucan backbone whose β-1,3-linked glucose units are substituted on their C-6 carbon by either glucose or N-acetylglucosamine residues. This is the first description of this type of structural motif in eukaryotic cell walls. Glucan-chitosaccharide fractions of A. euteiches induced the expression of defense marker genes in Medicago truncatula seedlings independently from the presence of a functional Nod Factor Perception protein. Furthermore, one of the glucan-chitosaccharide fractions elicited calcium oscillations in the nucleus of root cells. In contrast to the asymmetric oscillatory calcium spiking induced by symbiotic lipochitooligosaccharides, this response depends neither on the Nod Factor Perception protein nor on the common symbiotic pathway. These findings open new perspectives in oomycete cell wall biology and elicitor recognition and signaling in legumes.
authors.affiliation: Laboratoire de Recherche en Sciences Végétales (UMR 5546), Université de Toulouse (UPS), Castanet-Tolosan, France ; UMR5546, CNRS, Castanet-Tolosan, France.
authors.forename: Amaury
authors.initials: A
authors.lastname: Nars
authors.forename: Claude
authors.initials: C
authors.lastname: Lafitte
authors.forename: Mireille
authors.initials: M
authors.lastname: Chabaud
authors.forename: Sophie
authors.initials: S
authors.lastname: Drouillard
authors.forename: Hugo
authors.initials: H
authors.lastname: Mélida
authors.forename: Saïda
authors.initials: S
authors.lastname: Danoun
authors.forename: Tinaig
authors.initials: T
authors.lastname: Le Costaouëc
authors.forename: Thomas
authors.initials: T
authors.lastname: Rey
authors.forename: Julie
authors.initials: J
authors.lastname: Benedetti
authors.forename: Vincent
authors.initials: V
authors.lastname: Bulone
authors.forename: David George
authors.initials: DG
authors.lastname: Barker
authors.forename: Jean-Jacques
authors.initials: JJ
authors.lastname: Bono
authors.forename: Bernard
authors.initials: B
authors.lastname: Dumas
authors.forename: Christophe
authors.initials: C
authors.lastname: Jacquet
authors.forename: Laurent
authors.initials: L
authors.lastname: Heux
authors.forename: Judith
authors.initials: J
authors.lastname: Fliegmann
authors.forename: Arnaud
authors.initials: A
authors.lastname: Bottin
mesh_terms: D000117:Acetylglucosamine / Q000378:metabolism; D044744:Aphanomyces / Q000166:cytology*; D020013:Calcium Signaling / Q000187:drug effects* / Q000235:genetics; D002467:Cell Nucleus / Q000187:drug effects / Q000378:metabolism; D002473:Cell Wall / Q000737:chemistry*; D002686:Chitin / Q000737:chemistry / Q000494:pharmacology*; D002850:Chromatography, Gel; D018506:Gene Expression Regulation, Plant / Q000187:drug effects; D017343:Genes, Plant; D005936:Glucans / Q000737:chemistry / Q000494:pharmacology*; D054884:Host-Pathogen Interactions / Q000235:genetics / Q000276:immunology; D009682:Magnetic Resonance Spectroscopy; D013058:Mass Spectrometry; D046913:Medicago truncatula / Q000235:genetics* / Q000276:immunology* / Q000382:microbiology; D008958:Models, Molecular; D019441:Plant Epidermis / Q000166:cytology / Q000187:drug effects; D018517:Plant Roots / Q000166:cytology / Q000187:drug effects
chemical_list: D005936:Glucans; D002686:Chitin; D000117:Acetylglucosamine